Hybrid Coded Audio Data Streaming Apparatus and Method

1. An audio encoder comprising a combination of hardware and software elements arranged to receive an input signal comprising a stream of un-encoded audio data samples and to produce an output signal comprising a stream of encoded audio data samples, the hardware and software elements being configured to arrange said audio data samples into a plurality of data frames, and to further arrange each frame into at least one slice, each slice comprising a respective part of at least one spectral component of the input signal, the hardware and software elements further being arranged, in respect of a data frame of said output signal, to determine an achieved bit rate that is indicative of the actual bit rate of said data frame, and to calculate a target frame size for a subsequent data frame by comparing said achieved bit rate against a target bit rate, and wherein said hardware and software elements are is arranged to determine a respective spectral component bit allocation for the or each slice of said subsequent frame based on said target frame size, said spectral component bit allocation comprising a respective bit allocation for said at least one spectral component of the input signal, the hardware and software elements further being arranged to determine a respective dynamic range for said at least one spectral component of the input signal in respect of said subsequent frame, and to compare said respective dynamic range with said respective spectral component bit allocation, the hardware and software elements including a quantizer arranged to receive said at least one spectral component of the input signal in respect of said subsequent frame and to selectably quantize or not quantize said received spectral components depending on comparison of said respective dynamic range with said respective spectral component bit allocation.

2. An encoder as claimed in claim 1 , wherein said quantizer is arranged not to quantize said spectral components if said comparison of said respective dynamic range with said respective spectral component bit allocation indicates that said respective dynamic range can be losslessly accommodated by said respective spectral component bit allocation.

3. An encoder as claimed in claim 1 , wherein said quantizer is arranged to quantize said spectral components if said comparison of said respective dynamic range with said respective spectral component bit allocation indicates that said respective dynamic range cannot be losslessly accommodated by said respective spectral component bit allocation.

4. An encoder as claimed in claim 1 , wherein said quantizer is configured to support a plurality of selectable quantization methods, the encoder being arranged to select one or other of said quantization methods for application to said received spectral components depending on said comparison of said respective dynamic range with said respective spectral component bit allocation.

5. An encoder as claimed in claim 4 , wherein each quantization method is configured to apply a respective different level of quantization.

6. An encoder as claimed in claim 4 , wherein one of said quantization methods is configured to apply no quantization.

7. An encoder as claimed in claim 4 , wherein said encoder is arranged to select one or other of said quantization methods for application to said received spectral components depending on the extent by which the number of bits required to accommodate the respective dynamic range exceeds the respective spectral component bit allocation.

8. An encoder as claimed in claim 4 , wherein at least one of said quantization methods comprises a non-adaptive uniform scalar quantization method.

9. An encoder as claimed in claim 4 , wherein at least one of said quantization methods comprises a truncation function.

10. An encoder as claimed in claim 1 , wherein in order to calculate said respective spectral component bit allocation for each spectral component, said encoder is arranged to assign a respective lossless bit allocation to each spectral component, said lossless bit allocation corresponding to the respective dynamic range of the spectral component, to compare the total of the lossless bit allocations with a total bit allocation for the respective slice and, if the total of the lossless bit allocations exceeds the total bit allocation for the respective slice, to reduce one or more of the respective lossless bit allocations until the total of the initial bit allocations does not exceed the total bit allocation for the respective slice.

11. An encoder as claimed in claim 10 , wherein said encoder is arranged to reduce the bit allocation of one or more spectral components in an order corresponding to a weighting of said spectral components, wherein said weighting is preferably determined by the relative perceptual significance of said spectral components to a human listener.

12. An encoder as claimed in claim 10 , wherein if the total of the lossless bit allocations does not exceed the total bit allocation for the respective slice, the encoder is configured to use said lossless bit allocations as said spectral component bit allocations.

13. An encoder as claimed in claim 11 , wherein during said reduction of bits, one or more bits are removed from the respective bit allocation of one or more spectral components deemed to be of relatively low perceptual significance.

14. An encoder as claimed in claim 1 , wherein the encoder includes a pre-quantization coder arranged to apply one or more data compression methods, preferably lossless data compression methods, to said un-encoded audio data samples.

15. An encoder as claimed in claim 1 , wherein the encoder includes a pre-quantization coder arranged to apply a spectral decomposition transform, preferably a lossless transform, to said un-encoded audio data samples to produce a plurality of spectral audio data components.

16. An encoder as claimed in claim 15 , wherein each spectral component comprises a respective spectral audio data component.

17. An encoder as claimed in claim 16 , wherein said input signal comprises a plurality of audio channels, said encoder being arranged to perform said spectral decomposition in respect of each channel, each spectral component comprising a respective spectral audio data component of a respective channel.

18. An encoder as claimed in claim 1 , wherein said input signal comprises a plurality of audio channels, said encoder including a pre-quantization coder arranged to perform inter-channel or intra-channel decorrelation of said channels.

19. An encoder as claimed in claim 1 , wherein the encoder includes a post-quantization coder arranged to apply one or more data compression methods, preferably lossless data compression methods, to the quantized audio data samples.

20. An encoder as claimed in claim 1 , wherein said input signal comprises a plurality of audio channels, said encoder including a post-quantization coder arranged to perform inter-channel or intra-channel decorrelation of said channels.

21. An audio data compression system comprising an encoder as claimed in claim 1 and a decoder arranged for communication with one another across a communications link.

22. An audio encoder comprising hardware programmed by computer software to encode an audio input signal received by said hardware, said audio input signal comprising a stream of un-encoded audio data samples, and to produce an output signal comprising a stream of encoded audio data samples, the computer software causing the hardware to perform a method comprising: arranging said audio data samples into a plurality of data frames, and to further arrange each frame into at least one slice, each slice comprising a respective part of at least one spectral component of the input signal, determining, in respect of a data frame of said output signal, an achieved bit rate that is indicative of the actual bit rate of said data frame, and to calculate a target frame size for a subsequent data frame by comparing said achieved bit rate against a target bit rate, determining a respective spectral component bit allocation for the or each slice of said subsequent frame based on said target frame size, said spectral component bit allocation comprising a respective bit allocation for said at least one spectral component of the input signal, determining a respective dynamic range for said at least one spectral component of the input signal in respect of said subsequent frame, and to compare said respective dynamic range with said respective spectral component bit allocation, selecting to quantize or not quantize at least one spectral component of the input signal in respect of said subsequent frame depending on comparison of said respective dynamic range with said respective spectral component bit allocation.

23. An audio encoder comprising hardware elements arranged to receive an input signal comprising a stream of un-encoded audio data samples and to produce an output signal comprising a stream of encoded audio data samples, the hardware elements being configured to arrange said audio data samples into a plurality of data frames, and to further arrange each frame into at least one slice, each slice comprising a respective part of at least one spectral component of the input signal, the hardware elements further being arranged, in respect of a data frame of said output signal, to determine an achieved bit rate that is indicative of the actual bit rate of said data frame, and to calculate a target frame size for a subsequent data frame by comparing said achieved bit rate against a target bit rate, and wherein said hardware elements are arranged to determine a respective spectral component bit allocation for the or each slice of said subsequent frame based on said target frame size, said spectral component bit allocation comprising a respective bit allocation for said at least one spectral component of the input signal, the hardware elements further being arranged to determine a respective dynamic range for said at least one spectral component of the input signal in respect of said subsequent frame, and to compare said respective dynamic range with said respective spectral component bit allocation, the hardware elements including a quantizer arranged to receive said at least one spectral component of the input signal in respect of said subsequent frame and to selectably quantize or not quantize said received spectral components depending on comparison of said respective dynamic range with said respective spectral component bit allocation.